Project Description
Hexagonal Profile, Precision Bore — Built for Torque, Fit, and Fatigue
When a rotating assembly demands both positive anti-rotation grip and a smooth precision bore, the hexagonal outside round inside (HORI) seamless steel tube is the profile that answers. Its six-flat exterior locks into mating hexagonal sockets, wrench flats, and machined housings — eliminating slippage without the complexity of keyways, splines, or pinned joints. The round internal bore, drawn to tight dimensional control, provides an ideal passage for fluids, a precision seat for bearings, or a clean surface for subsequent honing and machining.
Fushun Steel Tube supplies HORI tubes as cold-drawn seamless products under EN 10305-1 and ASTM A519. Available in carbon, micro-alloyed, and Cr-Mo alloy grades, these tubes serve the automotive drivetrain, agricultural machinery hydraulics, and general mechanical engineering sectors.
Hexagonal Outside, Round Inside — The Shape That Works
The HORI profile is not a cosmetic choice. It solves real engineering problems across rotating, reciprocating, and fluid-handling assemblies:
- Anti-rotation without added parts
- The hexagonal exterior mates directly with a corresponding hex bore in the housing or bracket. Torque transfers through the full flat contact area, distributing load evenly and eliminating the stress concentration points that keyways and set screws create.
- Material and machining savings
- Instead of starting with a solid hex bar and gun-drilling a round bore — a process that removes 50–70% of the material — the HORI tube arrives near-net-shape. This can cut raw material cost and cycle time by 30% or more compared to solid-bar machining.
- Weight reduction in rotating assemblies
- A hollow profile inherently weighs less than a solid hex bar of the same across-flats dimension, yet the cold-drawn wall retains the strength required for torque transmission. In agricultural PTO shafts, automotive steering columns, and rotating machinery spindles, this weight saving translates directly to lower inertia and reduced power consumption.
- Consistent wall thickness for balanced rotation
- Cold drawing over a mandrel ensures uniform wall thickness around the entire circumference. This concentricity is critical for components that spin at high RPM — an unbalanced tube introduces vibration that accelerates bearing wear and shortens service life.
Applications Across Automotive, Agricultural, and General Machinery
Automotive & Commercial Vehicles
- Steering columns and intermediate shafts — hex OD locks into the collapsible column assembly; round ID accepts the inner shaft for telescoping adjustment
- Shock absorber outer tubes — hex flats provide the mounting interface; smooth ID guides the piston rod
- Drive shaft sleeves and coupling hubs — torque transmitted through hex flats without separate keyways
- Thrust rod bushings and linkage tubes — hex profile prevents rotation inside the pressed housing
- Fuel injection and high-pressure oil lines — round ID maintains precise flow cross-section under pulsating pressure
Agricultural Machinery
- Hydraulic cylinder barrels for lift arms and implements — hex OD simplifies mounting in forged brackets; round ID is honed to Ra ≤ 0.4 μm for seal life
- PTO drive shaft tubes — hex exterior transmits torque in telescoping shaft assemblies; round ID guides the inner sliding member
- Steering linkage components in tractors and harvesters
- Boom and frame pivot bushings
General Machinery & Equipment
- Gearbox selector shafts and guide tubes
- Linear actuator housings — hex exterior clamped in place; round ID guides the internal piston
- Pneumatic cylinder barrels for automation
- Precision spacer sleeves and bearing seats
- Hydraulic manifold tubes in mining and construction equipment
- Pump shaft sleeves and wear rings
Steel Grades — US & European Standards
Fushun Steel Tube stocks and produces HORI tubes in the grades most requested by global OEMs. The table below summarizes the principal options. Custom chemistries are available for project-specific requirements.
| Grade Family | ASTM / AISI | EN 10305-1 | Typical Condition | Key Attributes |
|---|---|---|---|---|
| Low-carbon | 1020 | E235 | +C, +N | Good formability, weldable, moderate strength |
| Medium-carbon | 1045 | C45E / E355 | +C, +SR, Q+T | Higher strength, good machinability after normalizing |
| Cr-Mo alloy | 4130 | 25CrMo4 | +C, Q+T | High strength with good toughness, deep hardenable |
| Cr-Mo alloy | 4140 | 42CrMo4 | Q+T | Highest strength and wear resistance of the standard range |
| Ni-Cr-Mo alloy | 8620 | 20NiCrMo2 | +C, case-hardened | Excellent core toughness with hard case after carburizing |
Need a grade not listed? Fushun Steel Tube’s metallurgical team can develop custom heats with tailored C, Mn, Cr, Mo, and Ni content. Yield strengths from 350 MPa to over 1200 MPa are achievable through controlled chemistry and heat treatment. Contact us for a free quote.
Specifications & Applicable Standards
| Standard | Scope |
|---|---|
| EN 10305-1 | Steel tubes for precision applications — cold drawn seamless, technical delivery conditions |
| ASTM A519 | Seamless carbon and alloy steel mechanical tubing |
| DIN 2391 | Seamless precision steel tubes (historical, still widely referenced) |
| BS 6323-4 | Seamless steel tubes for mechanical and general engineering |
| ISO 10799 | Cold-finished welded and seamless steel tubes for structural purposes |
Third-party certification to SGS, TÜV, or Bureau Veritas standards is available on request. All material ships with EN 10204 3.1 certificates as standard; 3.2 certificates can be arranged.
Dimensional Range & Delivery
| Parameter | Range |
|---|---|
| Across-flats (hex OD) | 10 mm – 108 mm (standard); up to 420 mm custom |
| Wall thickness | 1 mm – 20 mm (standard); up to 55 mm custom |
| Length | 3 m – 12 m fixed; cut-to-length available |
| Tolerance class (across-flats) | h8 – h10 (ISO 286) |
| Wall thickness tolerance | ±0.1 mm (precision); ±5% (standard) |
| Straightness | ≤ 0.5 mm per meter |
Stock & Lead Times: Common grades in standard sizes are available from ready stock with dispatch within 7 working days. Non-standard dimensions or special grades: MOQ 2–3 tons, delivery 25–35 days. Large-volume OEM programs receive competitive pricing with negotiated call-off schedules.
Manufacturing — From Billet to Finished Profile
- Steelmaking
- All material starts from electric arc furnace (EAF) heats, refined through ladle furnace (LF) and vacuum degassed (VD) for cleanliness. For critical applications requiring ultra-low inclusion content, electroslag remelting (ESR) or vacuum induction melting plus vacuum arc remelting (VIM+VAR) routes are available.
- Tube forming
- Hot-rolled seamless shells are produced by piercing round billets, then rolling and sizing to an intermediate round tube. The hot-rolled shell is annealed and pickled to prepare the surface for cold working.
- Cold drawing to the hex profile
- The round shell is drawn through a hexagonal die over a mandrel in one or multiple passes. This process simultaneously forms the hexagonal exterior, sizes the round interior bore, and work-hardens the material. The result is a tube that arrives near-net-shape with bright surface finish and tightly controlled dimensions. For precision applications, see our cold-rolled tube capabilities.
- Post-draw processing
- Depending on the grade and end-use, tubes may be stress-relieved, normalized, or quenched-and-tempered. Honing of the internal bore to Ra ≤ 0.4 μm is available for hydraulic applications. Ends can be chamfered, faced, or threaded per customer drawing.
Surface Finish & Tolerances
Cold-drawn HORI tubes leave the die with a smooth, bright surface free of mill scale. The standard as-drawn finish is suitable for most mechanical applications without further treatment.
| Feature | Specification |
|---|---|
| Exterior surface | Bright, cold-drawn; pickled and oiled option available |
| Internal surface roughness (as-drawn) | Ra ≤ 0.8 μm |
| Internal surface roughness (honed) | Ra ≤ 0.4 μm |
| Across-flats tolerance | h8, h9, or h10 per customer requirement |
| Wall thickness uniformity | ±0.1 mm achievable on precision-class tubes |
| End finish | Mill-cut; chamfered, faced, or threaded optional |
Corrosion protection — anti-rust oil, phosphating, or galvanizing — can be applied to customer specification. Stainless steel options are available for corrosive environments.
Quality Assurance & Testing
Every production batch passes through a gated quality workflow:
- Incoming billet verification — 100% spectrometer check of chemical composition
- In-process monitoring — online wall thickness and across-flats measurement during cold drawing
- Finished product testing:
- Dimensional verification (AF, ID, WT, straightness, length) per sampling plan
- Mechanical testing: tensile (Rm, Rp0.2, A%), hardness (HBW/HRC), impact (KV₂) as required
- Non-destructive testing: eddy current (ET) and ultrasonic (UT) per EN 10246 / ASTM E213
- Metallographic examination for grain size, decarburization, and inclusion content
- Flattening and flaring tests where applicable
- Certification — EN 10204 3.1 as standard; 3.2 with third-party witness available
- Optional — SGS, TÜV, BV independent inspection
Fushun Steel Tube is ISO 9001 certified and operates an IATF 16949-compliant quality management system for automotive-grade products.
Packaging & Shipping
- Standard packaging: anti-rust oil coating + individual plastic end caps + bundled with steel strapping
- Precision/Honed tubes: VCI anti-corrosion paper wrap + wooden cases or reinforced steel crates
- Custom packaging: customer-specific labeling, barcoding, and shipping marks supported
- Transport modes: sea freight (FCL/LCL), air freight, and road/rail for landlocked destinations
Frequently Asked Questions
Can you produce non-standard across-flats dimensions?
Yes. Unlike stock-profile distributors, Fushun Steel Tube operates its own cold-drawing lines. Non-standard hex sizes, thin-wall or heavy-wall variants, and custom profiles are routine. Provide your drawing and we will quote within 48 hours.
What is the minimum order quantity?
For common grades in standard sizes, 2–3 tons. For specialty alloys, high-precision tolerances, or custom profiles, small trial lots are accepted. Large OEM programs are quoted with volume-adjusted pricing.
Can you supply the tube in quenched-and-tempered condition?
Absolutely. 4130 (25CrMo4) and 4140 (42CrMo4) tubes are routinely supplied in Q+T condition with hardness and tensile properties specified to your requirements. The heat treatment is performed after cold drawing to preserve dimensional accuracy.
Do you offer internal honing?
Yes. For hydraulic cylinder applications, the round ID can be honed to Ra ≤ 0.4 μm with tight diametral tolerance, ready for seal assembly. Combined with the hex OD, this makes a complete near-net-shape hydraulic barrel.
How do you ensure the hex and bore are concentric?
Cold drawing over a fixed mandrel naturally centers the bore within the hex profile. We verify concentricity on every batch with wall-thickness measurements at six angular positions around the hex flats.
Get the Profile That Works
Whether you are designing a new steering column, shaving weight from a PTO drive shaft, or looking for a precision hex-bore tube to replace a machined-from-solid component, Fushun Steel Tube has the metallurgy, the tooling, and the experience to deliver.
